1. Field of Invention
This invention relates to polymer films. More particularly, this invention relates to ultrathin, polyimide polymer films and their production.
2. Prior Art
In U.S. Pat. No. 3,673,145, a process for preparing polyimide solutions that can be cast as films is disclosed. However, the disclosed films have thicknesses between 15 microns (i.e. 150,000 angstroms) and 80 microns (i.e. 800,000 angstroms) and cannot, therefore, be classified as ultrathin polyimide films.
In U.S. Pat. No. 2,867,609 void-free films allegedly prepared from polypyromellitimides are disclosed. However, no film thicknesses are disclosed.
In U.S. Pat. No. 2,710,853, polypyromellitimide films having thicknesses of three to seven mils are disclosed. However, the films are not ultrathin.
In U.S. Pat. No. 3,179,614, polyamide-acid films having thicknesses of 0.1 to 1.0 mils are converted to polyimide films by either heating the films or by treating them with acetic anhydride and pyridine. Such films, however, are not ultrathin.
Similarly, in U.S. Pat. Nos. 3,179,633 and 3,179,634, polyamide-acid films having thicknesses between 0.1 and 7 mils are thermally or chemically converted to polyimide films.
In U.S. Pat. No. 2,760,233, a process is disclosed for preparing curved polymer sheets from polyimide polymers. However, polyimide films are not disclosed nor are specific solvent mixtures and ratios suitable for casting ultrathin, pinhole-free, polyimide films disclosed.
U.S. Pat. No. 3,551,244 discloses a process for preparing on a water surface films having thicknesses between 0.05 and 5.0 microns (i.e. between 500 and 50,000 angstroms). The patent discloses that certain halogenated solvents, such as chlorobenzene, are suitable casting solvents and states that polyamide films can be prepared. However, polyimide polymers are not disclosed as being suitable and no specific solvent mixtures and ratios suitable for casting pinhole-free polyimide films having thicknesses less than 400 angstroms are disclosed.
In U.S. Pat. No. 3,933,561, a process for preparing polymeric films on water is disclosed. The film thicknesses are usually less than about 2.5 microns (i.e. 25,000 angstroms) and thicknesses of less than 0.1 micron (i.e. 1000 angstroms) are allegedly achieved. While polyamides are allegedly suitable for the patent's process, polyimide films are not disclosed nor are specific solvent mixtures and ratios suitable for casting ultrathin polyimide films.
U.S. Pat. No. 3,767,737 discloses a method for producing nonporous polymer membranes having thicknesses between 0.005 and 0.05 mils on a support liquid. Any polymer capable of being cast as a film from solvents is asserted to be suitable for use in the patent's process. However, polyimides are not specifically listed as suitable polymers and specific mixtures of solvents and appropriate solvent ratios for preparing pinhole-free polyimide films having thicknesses of 400 angstroms or less are not disclosed.
U.S. Pat. Nos. 4,155,793, 4,279,855 and 4,374,891 disclose processes for preparing substantially void-free, ultrathin, permeable, polymeric membranes having a thickness of 500 angstroms or less. Organic and inorganic polymers are allegedly suitable for use in the patent's process. However, only films prepared from organopolysiloxane-polycarbonate interpolymers mixed with polyphenylene oxide are disclosed in the examples. Polyimide films are not disclosed nor are suitable solvent mixtures and ratios for casting polyimide films having thicknesses of 400 angstroms or less.
Other patents, such as U.S. Pat. Nos. 2,631,334, 2,689,187, and 4,393,113, also disclose ultrathin, polymeric films. However, polyimide films are not disclosed.
U.S. Pat. Nos. 3,356,648 and 3,959,350 disclose fluorinated polyimide films. However, no film thicknesses are disclosed, and a process for preparing ultrathin, pinhole-free, polyimide films is not disclosed.
U.S. Pat. No. 4,592,925 discloses fluorinated polyimide films having thicknesses of about 0.1 mil to about 0.5 mil (i.e., about 25,400 to about 127,000 angstroms). U.S. Pat. No. 4,645,824 discloses fluorinated polyimide films having thicknesses of about 0.1 mil to about 2.0 mils (i.e., about 25,400 to about 508,000 angstroms). Thus, these patents do not disclose ultrathin polyimide films.
Commonly-asigned U.S. patent application Ser. No. 07/217,928 discloses films having a thickness in the range of about 2 to about 3 mils prepared from copolyimides derived from 2,2-bis(aminophenyl) hexafluoropropane. Commonly-assigned U.S patent application Ser. No. 07/217,929 discloses that films having thicknesses of several mils can be prepared by high molecular weight polyimides containing hexafluoropropylidene linkages. Neither patent however, discloses the preparation of ultrathin films nor a means for preparing such films.
In the prior art, the preparation of ultrathin, pinhole-free, polyimide, free-standing films having thicknesses of less than 400 angstroms generally has not been disclosed. Usually, prior art polymer films having thicknesses of less than 400 angstroms contain voids and other macroscopic defects.
Therefore, it is an object of this invention to prepare ultrathin, polyimide polymer films.
It is a further object of this invention to prepare pinhole-free, polyimide polymeric films.
It is also an object of this invention to prepare free-standing, polyimide films having thicknesses of 400 angstroms or less.
These and other objects are obtained by the products and process of the present invention.